With the constantly accelerating crime rate and the inherent ingenuity of the criminal, citizens have employed many devices to augment their ability to identify a caller. For centuries peepholes of one sort or another have served to assist a dwelling's occupant in identifying potential entrants. The traditional peephole has been refined over the years. Refinements include the use of ultra-wide angle "fish-eye" lenses to enhance the field of view and various camouflages, like one-way glass, to conceal the observer within.
The urban apartment house in particular presents peculiar security problems. Not only may ambient hallway lighting be inadequate, but also irregularly-shaped hallways make ideal hiding places for persons seeking to avoid detection. If a perpetrator premeditatedly reduces visibility, most available viewing devices will simply fail to function, exposing the user to the difficult choice of opening the door to an intruder or preventing the entrance of a friend.
U.S. Pat. No. 3,973,835 issued to Miyakawa et al discloses a periscope device which includes a fixed one-way mirror. The viewer looks through the one-way mirror to achieve an axial view and by positioning the radial lens in the radial port accomplishes radial viewing. The fixed mirror acts as a filter and decreases the amount of available light reaching the eyepiece.
U.S. Pat. No. 4,050,792 issued to Svensson discloses a viewing device which is comprised of a housing and three separate viewing elements which afford a panoramic view. The field of view is inherently limited by the placement of the individual viewing elements, making right-angle viewing unobtainable. Moreover, the separate viewing elements require the viewer to align his line of sight through three separate apertures. Finally, the construction of the device would encourage the spread of fire. The mounting hole, cut through the door, could act as a sizable chimney drawing flames therethrough.